why new software cant run in old hardware

[raaaid]

lets take this game would it be posible to run it in rasperry pi at cpu700mhz with 256 ram?

i say if the devs want it would be posible

make it 16 colours instead of 32 million, hey i paint with less

make the posibility to make all ground just blue and green and brwon of buildings

take all shades away

well you know...

so if its posible to have a toned down game as to run it in low end pc why they dont give us that option and force us to buy new hardware?